1. Technical Field
The present invention relates generally to integrated circuit design, and more particularly, to selectively scaling an integrated circuit design layout by: layer, region or cell, or a combination of these, for the purposes of increasing yield in early processes in such a way that hierarchy is preserved.
2. Related Art
One way of modifying an existing very large scale integrated (VLSI) circuit design to increase its manufacturing yield is to spread wires and add redundant vias in order to decrease critical area and increase via reliability. However, in the early stages of a new manufacturing process, these post-layout modifications alone may not be sufficient to achieve the desired yield improvement. Another yield-enhancing modification to an existing layout is to relax the spacing and width tolerances, which can be accomplished by a geometric scaling process. A challenge arises, however, when this scaling is attempted on only certain design layers and in the presence of certain other geometric constraints or in the presence of hierarchy. For example, back-end-of-line (BEOL) layers might be chosen for scaling but without altering any device sizes, and with the requirement that the location of connections from the top-level wiring to the integrated-circuit package remain fixed.
A simple linear geometric scaling (i.e., multiplying the coordinates of every object in the design database by a fixed scaling factor) is obviously inadequate if connectivity is to be maintained between layers that are scaled and layers that are not scaled. The problem of hierarchical scaling itself is difficult to solve. One approach is addressed in co-pending U.S. patent application Ser. No. 10/438,625 (currently pending), entitled “A Practical Method for Hierarchical-Preserving Layout Optimization of Integrated Circuit Layout,” which is hereby incorporated by reference. Another approach is selective scaling, an example of which is disclosed in U.S. Pat. No. 6,756,242 to Regan. Regan, however, teaches scaling an entire design with different scaling factors in an X direction and a Y direction, which is also inadequate if connectivity is to be maintained between layers.
In semiconductor manufacturing, design layouts are completed with a set of fixed ground rules that are provided to the designers by the manufacturing organization. The ground rules describe process and lithography best estimates of what is manufacturable. The ground rules attempt to balance chip density on a wafer (aggressiveness) with what can be reliably manufactured (conservatism). During the lifetime of a technology process or a design, “learning” takes place through failure analysis on finished products and in the manufacturing line. If implemented, this learning can improve yields. For example, the ground rules may change to reflect the yield learning. Unfortunately, frequent or considerable changes cannot usually be made because implementation of any change is expensive because each requires designer involvement in modifying the design to reflect the new ground rules. More significantly, any design modification typically requires new masks, which are extremely expensive. Accordingly, design changes are historically only made very infrequently. Yield related design changes may be added if functional changes require new masks (i.e., if there are difficulties with the function or performance which require a new design iteration), or if there are significant yield issues which force a new design iteration in order to achieve cost targets.
Future manufacturing and design environments, however, provide several important aspects that may allow significant improvement of this process: First, maskless lithography has been proposed for future technologies, which if implemented will eliminate the costs of additional mask sets for a changed design. Second, improved simulation and validation capabilities may provide the ability to do more “full-up” simulations of designs because of improved algorithms, parallel processing, and system architectures. In this fashion, selective scaling may be applied in a tightly coupled feedback loop with the manufacturing line with process and yield feedback, during the life of a design. In current manufacturing and design environments, limited mask lifespans offer the opportunity for periodic layout updates during the life of a design.
In view of the foregoing, there is a need in the art to address the problems of the related art.